Nicholas J. Mourlas

PECVD silicon carbide as a chemically resistant material for micromachined transducers

Abstract Plasma enhanced chemical vapor deposited (PECVD) amorphous hydrogenated silicon carbide is a material with many potential applications for micromachined transducers. Specifically, its resistance to etching in a broad range of media such as sulfuric acid/peroxide, hydrofluoric acid and potassium hydroxide make it an excellent choice for use as an encapsulating material for media compatible transducers. This etch resistance also makes it useful as a masking material for intermediate processing steps. Despite this wet chemical resistance, it can be patterned easily in fluorine-based plasmas. A series of trials were undertaken in an attempt to correlate stress, resistivity and wet etch resistance with the following deposition parameters: pressure, CH4 flow rate, low frequency power, low frequency cycle time, high frequency power, and high frequency cycle time. Work to date has demonstrated a CMOS compatible, insulating thin film with a low stress (

PECVD silicon carbide for micromachined transducers

We report preliminary work on PECVD amorphous hydrogenated silicon carbide (a-SiC:H) as a material with many potential applications in micromachined transducers. Four examples are presented: an electrochemical probe; a fully packaged, encapsulated pressure sensor; a sealed and coated microfluidic channel; and deep etched channels in glass. A designed experiment was undertaken in an attempt to correlate stress, resistivity and wet etchability with the following process parameters: pressure, CH/sub 4/ flow rate, low frequency power, low frequency cycle time, high frequency power, and high frequency cycle time. While this preliminary work does demonstrate a CMOS compatible, insulating thin film with low stress (<100 MPa compressive), high etch resistance, and conformal coating, the complexity of the plasma chemistry will require further investigation to elaborate parameter dependencies.

Novel Interconnection and Channel Technologies for Microfluidics

The growth of microfluidic applications for medical diagnostics and biological and chemical assays has created a need for fundamental building blocks from which fluidic systems can be constructed. This work discusses two of these building blocks: 1) interconnects for interfacing monolithic microfluidic systems to standard capillary tubing, and 2) conformal coating procedures for microfluidic channels using plasma enhanced chemical vapor deposited (PECVD) silicon carbide (SiC).

Direct Visualization of Cardiac Radiofrequency Ablation Lesions

Effective ablation of atrial fibrillation and other cardiac arrhythmias requires precise catheter navigation and controlled delivery of energy to cardiac tissue. In this study, we summarize our initial experience using a fiber optic direct visualization catheter to evaluate and guide placement of endocardial radiofrequency (RF) ablation lesions. RF lesions were created in cadaveric porcine hearts and examined in a blood-filled field using a direct visualization catheter. Direct visualization of RF lesions was repeated in vivo using an ovine model. Lesions and interlesion gaps were clearly identifiable using the direct visualization catheter. It was possible to place lesions in proximity to anatomical landmarks and in relation to one another. Catheter-generated images correlated well with lesion appearance on gross examination. Direct catheter-based visualization is a feasible technique for guiding RF lesion placement, estimating lesion size, and identifying interlesion gaps. Future work is needed to correlate surface appearance with transmurality and electrical isolation.

An In-Line Osmometer for Application in Tissue Based Biosensor Systems

Analysis tools that use living cells as the primary sensor element require samples be adjusted to physiological osmolarity levels prior to evaluation. This work demonstrates an in-line osmometer for the purpose of evaluating the baseline osmolarity of a sample prior to adjustment. The operational range of the device presented is 16 – 500 mOsm/kg with a resolution of 25 mOsm/kg and an accuracy of ± 45 mOsm/kg.